1. Field of the Invention
The present invention relates to a heat recovering technique for recovering exhaust heat, and relates to an exhaust heat recovering method, an exhaust heat recovering apparatus and a cogeneration system that recover exhaust heat from a heat source generating exhaust air, for example, an engine and from the exhaust air to store the heat in a heat medium such as hot water.
2. Description of the Related Art
Conventionally, a dynamo which uses an engine fueled by fuel gas as a power source is known. The engine driving the dynamo generates heat according to combustion of fuel. An exhaust heat recovering apparatus recovering and using exhaust heat from the generated heat is in practical use.
Concerning such exhaust heat recovering, it is known that heat of exhaust air from an engine, and condensation heat thereof are recovered (for example, Japanese Laid-open Patent Publication No. 2001-123885).
Recovering the condensation heat from exhaust air (Japanese Laid-open Patent Publication No. 2001-123885) is recovering latent heat in exhaust gas. In this exhaust heat recovering apparatus, a heat medium sent out by a pump exchanges heat with engine oil, exchanges heat with exhaust air in a heat exchanger, then further exchanges heat with an engine along with cooling down the engine to store the recovered heat in a heat storage tank. In this case, the temperature of the heat medium is set low so that the temperature of the water vapor in the exhaust air from which heat is exchanged stays lower than the dew point to recover condensation heat (latent heat) in the exhaust air to the heat medium.
Even if the temperature of the heat medium introduced into the heat exchanger is controlled low, some degrees of a temperature is required by an introduced temperature to an engine cooling unit in order to protect the engine. Therefore, it is necessary for raising the temperature of the heat medium in the heat exchanger to restrict the flow rate of the heat medium. If the flow rate of the heat medium is restricted, the temperature in heat exchange with the engine oil rises more substantially. Thus, it becomes difficult to introduce the heat medium to the heat exchanger at an expected temperature.
In power generation using an engine, when surplus power is generated, the electricity is converted to heat by a heater, etc. to be recovered. There is inconvenience, if the heater is disposed in a heat medium circuit, that the heat medium is boiled in a heating unit by heater heat generation when the flow rate of the heat medium is low.
Concerning such problems, there is no disclosure nor suggestion thereof in Japanese Laid-open Patent Publication No. 2001-123885, and no disclosure nor suggestion about structure, etc. solving them are presented therein.